1*19c3b8c2SApple OSS Distributions<h2>device_read_async</h2> 2*19c3b8c2SApple OSS Distributions<hr> 3*19c3b8c2SApple OSS Distributions<p> 4*19c3b8c2SApple OSS Distributions<strong>System Trap</strong> - Read a sequence of bytes from a device object. 5*19c3b8c2SApple OSS Distributions<h3>SYNOPSIS</h3> 6*19c3b8c2SApple OSS Distributions<pre> 7*19c3b8c2SApple OSS Distributions<strong>kern_return_t device_read_async</strong> 8*19c3b8c2SApple OSS Distributions <strong>(mach_port_t</strong> <var>device</var>, 9*19c3b8c2SApple OSS Distributions <strong>mach_port_t</strong> <var>queue</var>, 10*19c3b8c2SApple OSS Distributions <strong>mach_port_t</strong> <var>request_id</var>, 11*19c3b8c2SApple OSS Distributions <strong>dev_mode_t</strong> <var>mode</var>, 12*19c3b8c2SApple OSS Distributions <strong>recnum_t</strong> <var>recnum</var>, 13*19c3b8c2SApple OSS Distributions <strong>io_buf_len_t</strong> <var>bytes_wanted</var><strong>);</strong> 14*19c3b8c2SApple OSS Distributions</pre> 15*19c3b8c2SApple OSS Distributions<h3>PARAMETERS</h3> 16*19c3b8c2SApple OSS Distributions<dl> 17*19c3b8c2SApple OSS Distributions<p> 18*19c3b8c2SApple OSS Distributions<dt> <var>device</var> 19*19c3b8c2SApple OSS Distributions<dd> 20*19c3b8c2SApple OSS Distributions[in device send right] A device port to the device to be read. 21*19c3b8c2SApple OSS Distributions<p> 22*19c3b8c2SApple OSS Distributions<dt> <var>queue</var> 23*19c3b8c2SApple OSS Distributions<dd> 24*19c3b8c2SApple OSS Distributions[in io_done queue send right] The port returned from 25*19c3b8c2SApple OSS Distributionsio_done_queue_create. 26*19c3b8c2SApple OSS Distributions<p> 27*19c3b8c2SApple OSS Distributions<dt> <var>request_id</var> 28*19c3b8c2SApple OSS Distributions<dd> 29*19c3b8c2SApple OSS Distributions[in send right] An unique request identifier that will be passed back as 30*19c3b8c2SApple OSS Distributionspart of the io_done_result structure. 31*19c3b8c2SApple OSS Distributions<p> 32*19c3b8c2SApple OSS Distributions<dt> <var>mode</var> 33*19c3b8c2SApple OSS Distributions<dd> 34*19c3b8c2SApple OSS Distributions[in scalar] I/O mode value. Meaningful options are: 35*19c3b8c2SApple OSS Distributions<p> 36*19c3b8c2SApple OSS Distributions <dl> 37*19c3b8c2SApple OSS Distributions<dt> <strong>D_NOWAIT</strong> 38*19c3b8c2SApple OSS Distributions<dd> 39*19c3b8c2SApple OSS DistributionsDo not wait if data is unavailable. 40*19c3b8c2SApple OSS Distributions </dl> 41*19c3b8c2SApple OSS Distributions<p> 42*19c3b8c2SApple OSS Distributions<dt> <var>recnum</var> 43*19c3b8c2SApple OSS Distributions<dd> 44*19c3b8c2SApple OSS Distributions[in scalar] Record number to be read. 45*19c3b8c2SApple OSS Distributions<p> 46*19c3b8c2SApple OSS Distributions<dt> <var>bytes_wanted</var> 47*19c3b8c2SApple OSS Distributions<dd> 48*19c3b8c2SApple OSS Distributions[in scalar] Size of data transfer. 49*19c3b8c2SApple OSS Distributions</dl> 50*19c3b8c2SApple OSS Distributions<h3>DESCRIPTION</h3> 51*19c3b8c2SApple OSS Distributions<p> 52*19c3b8c2SApple OSS DistributionsThe <strong>device_read_async</strong> interface enqueues a read operation for a 53*19c3b8c2SApple OSS Distributionssequence of bytes from a device object. The meaning of recnum as well 54*19c3b8c2SApple OSS Distributionsas the specific operation performed is device dependent. 55*19c3b8c2SApple OSS Distributions<h3>RETURN VALUES</h3> 56*19c3b8c2SApple OSS Distributions<dl> 57*19c3b8c2SApple OSS Distributions<strong>device_read_async</strong> returns only invalid parameter errors. 58*19c3b8c2SApple OSS Distributions<dd> 59*19c3b8c2SApple OSS Distributions</dl> 60*19c3b8c2SApple OSS Distributions<h3>RELATED INFORMATION</h3> 61*19c3b8c2SApple OSS Distributions<p> 62*19c3b8c2SApple OSS DistributionsFunctions: 63*19c3b8c2SApple OSS Distributions<a href="device_read_async_inband.html"><strong>device_read_async_inband</strong></a>, 64*19c3b8c2SApple OSS Distributions<a href="DR_overwrite_async.html"><strong>device_read_overwrite_async</strong></a>, 65*19c3b8c2SApple OSS Distributions<a href="device_write_async.html"><strong>device_write_async</strong></a>, 66*19c3b8c2SApple OSS Distributions<a href="device_write_async_inband.html"><strong>device_write_async_inband</strong></a>, 67*19c3b8c2SApple OSS Distributions<a href="io_done_queue_create.html"><strong>io_done_queue_create</strong></a>. 68